Next Generation Adaptive Optics - Solar System Science Cases -

Next Generation Adaptive Optics

- Solar System Science Cases -

F. Marchis (UC-Berkeley)

Members:

A. Bouchez (Caltech), J. Emery (NASA-Ames), K. Noll (STSCI), M.

Adamkovics (UC-Berkeley)

SSC meeting - June 21-22 2006, Hawaii, USA

General introduction• AO expands the study of our solar system

– Good temporal monitoring to observe variable phenomena (atmosphere and surface)

– Short time scale to respond to transit and unpredictable events (impact of a comet on Jupiter)

• Keck Observatory and planetary sciencesignificant contributions and dynamic sub-field.Since 2000:– 32% of Keck referee papers.– 42% of all Keck press releases– NASA (1/6 partner of Keck Obs) supports investigations

mostly in Planetary science

Science Cases A few science cases were chosen to illustrate the

advanced capabilities of NGAO (with simulations)

• A. Binary Minor Planets– Detection and orbits of asteroidal satellites– Spectroscopy of moonlets– Size and shape

• B. Satellites of Giant Planets– Titan’s surface and its atmosphere– Io’s volcanism

Minor Planets• Building blocks of the Solar System linked to its formation•~400,000 minor planets known• Small apparent size (largest 1 Ceres, Dapp=0.7arcsec “seeing” limit)

Main-Belt

L4-Trojan

L5-Trojan

Centaurs TNOs

Diversity of shapes and sizes 25143 Itokawa

“Like archaeologists working to translate stone carvings left behind by ancient civilizations, the collisional and dynamical clues left behind in or derived from the Main

Belt, once properly interpreted, can be used to read the history of the inner Solar System.” Bottke et al 2005

What are asteroids made of?

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are needed to see this picture.

(a) Shape of NEA* Toutatis observed with radar

Internal structure?

(b) Monolith (c) Contact Binary(d) Rubble PileFrom E. Asphaug, 1999, “Survival of the weakest”

* NEA= Near Earth Asteroid

Binary AsteroidsA Family Portrait

~85 multiple asteroidal systems knownAstronomical prize for astronomers and theorists Mass, density, constraints on formation of planets

MB - Ida and Dactyl (Galileo 1993)

MB 87 Sylvia and its 2 moons (VLT AO, 2005)

MB -45 Eugenia &

Petit-Prince (CFHT AO, 1998)

TNOs 2003EL61 (Keck AO, 2005)

Multiple asteroidal systems and NGAO

• + better angular resolution in visible (~15 mas) -> close doublet (sep. < 50 mas) can be also studied

• + a better sensitivity as well…

Keck NGS

SR~40%, mv<13.5

Keck LGS

SR<20%, mv<17.5

Keck NGAO

SR>70%, mv<17.5

Percent of observable binary systems

<20% ~70% ~70%

Size ratio of smallest satellite at 0.6”

1/40-1/50 ~1/10-1/30 ~1/70-1/90

Considering 80 known multiple asteroidal systems:

NGAO capabilities

Simulation context:• 87 Sylvia was discovered in 2005: Rprimary = 143 km, RRemus= 3.5 km, RRomulus=9 km• Insert 2 more moonlets. One closer (6 km) at 480 km and one smaller (1.75 km) at 1050 km



Triple system 87 Sylvia with VLT/NACO Pseudo-Sylvia simulated

Simulations

Simulation of pseudo- Sylvia observed with various AO systems

1.6”

•Better sensitivityDetection of fainter moonlet & closer moonletsMore multiple systems

•Better photometry Better estimate of the size and shape of moonlet

•Better astrometry Reliable estimate of orbital parameters, small orders perturbations (e.g., precession, interactions between moonlets, …)

Trans-Neptunian Object satellite systems

• Most large TNOs may have multi-satellite systems, which record their formation and/or collisional history.

2003 EL61: A Charon-sized (~1500 km) TNO with 2 satellites in non-coplanar orbits (Brown et al. 2006).

Keck 2 LGS-AO

NGAO simulations

2003 EL61 at 51 AU

Identical system at 100 AU (mv=20), observed

using an off-axis V=16.5 NGS. & 50” separation

Hypothetical 3rd moon,75 km diameter.

K band -2”

K band -1”

K band -2”

• An NGAO survey of large TNOs would find all satellites >100 km diameter out to 100 AU.

Low resolution spectroscopy• Better AO correction higher SN on spectra of moons

and primary (capture body, infant of primary, age, …) • Visible wavelength range characterize the surface

composition

Silicate absorption bands centered at

1 and 2 m

Summary Science case A

• Keck NGAO will be the best tool for this scientific subject (no space mission scheduled, need for numerous observations,…)

• Density & composition of minor planet is the key to understanding the formation of the solar system

Science CasesA few science cases were chosen to illustrate the advanced

capabilities of NGAO (with simulations)

• A. Binary Minor Planets– Detection and Orbits of asteroidal satellites– Spectroscopy of moonlets– Size and shape

• B. Satellites of Giant Planets– Titan’s surface and its atmosphere– Io’s Volcanism

Volcanism of Io• The most volcanically active place in the solar system• Only 5 successful flybys with Galileo (spatial resolution of

global NIR observations 100-300 km)

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• Outstanding questions:- Internal composition linked to the highest temperature of magma- Evolution in the orbital resonance, constrained by the heat flow measurement and evolution

Io observed with NGAO in NIR

• Up to 0.9 m, thermal output of outburst can be detected (T>1450 K)• Up to 0.7 m -> mafic absorption band (centered at 1 m)• Thermal band imaging (3-5 m) capabilities are necessary

0.9”

Keck NGAO - H Band Keck NGS - H Band

FWHM=33 mas FWHM=44 mas

Comparison with HST

+ Better spatial resolution (~40 km) than Galileo spacecraft global NIR images• Surface Changes• Plumes

No future mission (with imaging capabilities) planned toward Jupiter (brief flyby in 2007 by New Horizons) NGAO on Keck is an highly competitive instrument!

Why do we need NGAO?

• Best angular resolution provided in visible and NIRDirectly image planetary surface and atmosphere, characterized by spectroscopy

• Excellent and stable Strehl ratio in NIR Detect moonlets around asteroids & KBOs and determine their orbits and spectra.

• A flexible AO system with service observing Maximize the scientific return and efficiency of the observatory and observe transient events or monitor regularly

The End

Other satellitesSatellite

name

Ang. Size

(mas)

Max Ang.

Sep.

(arcsec)

Mv comments

Mimas 60 30 13.0

Enceladus 80 39 11.6 Volcanic activity (science, 2006)

Tethys 170 48 10.4

Dione 180 61 10.5

Rhea 250 85 9.8

Titan 830 198 8.3 Cryo-volcanoes?

Iapetus 230 576 11.2

Io 1200 95 5.2 Basaltic volcanic activity

Europa 1000 150 6.3 Young surface - ocean beneath?

Ganymede 1700 240 5.6 Ocean?

Callisto 1600 420 6.9

Himalia 60 3000 15.7

Reminder: FWHM PSF(NGAO-R) = 14 mas

Other satellites


•Consider high resolution spectral analysis (R>1000) for atmospheric features. Example geysers on Enceladus•Problem due to giant planet halo contribution on the WFS?



80 mas



Other satellites


Insert here a figure showing which satellites can be observedconsidering the glare of the planetWe should use Van Dam et al. measuremnts (sent to Mate)

How many asteroids observable w/ NGAO?

Populations by brightness (numbered asteroids only)

Orbital type Total number

V < 15 15 < V < 16 16 < V < 17 17 < V < 18

Near Earth 424 346 50 25 3

Main Belt 118381 4074 9537 25330 45420

Trojan 1010 13 44 108 262

Centaur 31 0 1 2 2

TNO 108 0 0 0 2

Other 483 112 151 152 54

Mysterious Titan• Satellite of Saturn - D~5150 km

• Surface mostly hidden by an opaque prebiotic atmosphere

• Studied with Cassini spacecraft (4 flyby already) and Huygens lander (Jan. 2004)

• Spatial resolution of global observations up to 9km in NIRQuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.





Titan Surface and its Atmosphere• Goals: Observations of an extended object - imaging and

spectroscopy of its atmosphere. Comparison with previous NGS AO systems. Illustration of the variability of solar system phenomena (volcanism, clouds)

• Inputs from TCIS: Simulated short exposure ﾊ On-Axis PSFs (~2-4s) (x10) at various wavelength (NOT YET DEFINED) in good seeing conditions for a bright reference (mv=8.5). Should we expect a degradation due to the angular size of Titan (D=0.8") ﾊ

• Method:We will create a fake Titan observations considering also the haze component in visible and NIR and using global map (with R=30-200 km) of Cassini spacecraft. ﾊ We will focus on atmospheric windows for which the surface can ﾊ be seen (tools are ready MA & FM). Wavelength not defined yet.- Deconvolution with AIDA may be included (algorithm 95% ready FM)- Comparison with Keck NGS AO, VLT AO, and Cassini will be included- Good temporal coverage from the ground vs spacecraft will be discussed and illustrated by surface changes due to a cryo-volcano (and/or clouds in the troposphere?)- Spectroscopy to detect N2+ species in the atmosphere (high R) and measure winds in Titan atmosphere at various altitudes (extremely high R).

Titan Surface and its Atmosphere• First results - Comparison of H band observations



About the fake image of Titanbased on Cassini map at 0.94 m, 600 pixels across, spatial resolution of 9 km (1 mas) near disk center, Minnaert function reflectivity, long=150W, lat=23S

FWHM= 44 mas FWHM= 34 mas FWHM= 34 mas

0.8”

Titan Surface and its Atmosphere• Multi-wavelength observations

PSF used : NFAO - no blurring



cm

Atm. window

2.7

2.0

1.57

1.26

1.06

0.92

0.83

0.75

Prebiotic atmosphereNot completely transparent in visible-NIR

Titan Surface and its Atmosphere• Comparison HST-ACS/HRC & Keck NGAO

Clear progress in angular resolution compared with HST



Surface Changes on Titan

HST/ACS R

KNGAO-R

Cryovolcanic-style surface change are detectable with KNGAO in J band. In R band morphology is better estimated -> volcano caldera, lava flow?

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Next Generation Adaptive Optics - Solar System Science Cases -